I agree with not making a raggie quilt, for the reasons mentioned. The ones I have made range from 12" square, to 18" square. I recommend that you make more than one. They should be close to identical. If he really gets attached, you need one to use, one in the wash, one for the car, one for the diaper bag, one for the baby sitter, and one on standby. Mom should switch them out regularly, so they all get the same amount of wear.
How do I know this? My grandkids are now 6 and 7, and sleep with a very raggedy 'snuggle' blankie. My daughters hold their breath every time the blankie must be washed!